This invention relates to a magnetic head and a magnetic reproducing apparatus, and more particularly, to a magnetic head including a magnetic yoke having a projected portion toward a recording medium, and a magnetic reproducing apparatus incorporating the magnetic head.
Although HDDs (hard disk drives) have recently experienced epoch-making improvement in magnetic recording density, further enhancement of their recording density is still demanded. Along with the progressive downsizing of recording bits to cope with the continuous demand for higher and higher recording densities, conventional thin-film heads became insufficient in reproduction sensitivity, and surrendered its position as the main current to magnetoresistance effect (MR) heads making use of a magnetoresistance effect. Among these MR heads, spin valve giant magnetoresistance (SVGMR) heads are being remarked as exhibiting an especially large magnetoresistance effect.
On the other hand, along with enhancement of the recording density, floating amounts of thin-film magnetic heads during traveling are decreasing for detecting smaller medium bit magnetic fields. It is therefore predicted that magnetic heads will be inevitably driven in intermittent or continuous contact with recording mediums. Also from various viewpoints other than enhancement of the recording density, HDDs will be brought into use in AV (audio-visual) devices (such as video and/or audio recorders) as the multimedia era matures. When a HDD is borne in an AV device, reliability of HDD, especially its durability against external impact, is an important issue. If an external impact (such as mechanical shock or vibration) is applied, then the magnetic head may unexpectedly hit the medium surface. Therefore, there is a demand for development of magnetic heads resistant to physical contacts.
However, the above-indicated SVGMR heads are well known as exhibiting abnormal changes of resistance due to the heat generated by contact with recording mediums during reproduction (thermal asperity). Therefore, conventional MR heads and SVGMR heads whose magnetic detector portions are exposed on medium-facing surfaces of the magnetic heads may fail to follow the future enhancement of recording density.
In contrast, the use of a yoke-type magnetic head that includes a magnetic yoke for leading the signal magnetic field from the recording medium to an MR element is considered effective. Since the yoke-type magnetic head is so configured that the magnetic detector portion of the MR device is not exposed on the medium-facing surface, it is resistant to thermal asperity.
Taking those situations into consideration, it will be effective toward future enhancement of magnetic recording density to combine a yoke-type magnetic head and an MR element.
However, to ensure a signal magnetic flux from a minute recording bit to be read out with a high resolution, a projecting portion must be made at the tip of the magnetic yoke, that is, on the medium-facing surface. In other words, it is necessary to provide a minute projecting portion on the medium-facing surface of the magnetic yoke so as to draw up there the signal magnetic flux from the recording bit with a high resolution.
However, as a result of the Inventors' own researches, the yoke-type magnetic head having such a projecting portion was found to involve the magnetic domain generated at the projecting portion of the magnetic yoke as another large factor of noise in addition to the MR element.
FIGS. 18A and 18B are schematic diagrams that show the structure of a yoke-type magnetic head prepared and evaluated by the Inventors in the way toward the present invention. FIG. 18A is its perspective view, and FIG. 18B is its longitudinal cross-sectional view.
The magnetic head shown here includes a pair of magnetic yoke layers 2, 2 formed on a substrate 12 to face to a recording medium, not shown, in alignment with each other via a magnetic gap 1. A magnetoresistance effect film 4 underlies the magnetic yoke layers 2, 2, and a lower electrode 7 and an upper electrode 8 are connected to supply a sense current perpendicularly to the film plane.
In this yoke-type magnetic head, the pair of magnetic yoke layers are magnetically coupled to the magnetoresistance effect film 4 to form a magnetic circuit, and detect a signal magnetic flux led from the recording medium to the magnetoresistance effect film.
For the purpose of detecting a signal from a minute recording bit of a recording medium, not shown, while distinguishing it from those of adjacent recording bits, each magnetic yoke layer 2 has a projecting portion 2A of a predetermined size. More specifically, as shown in FIGS. 18A and 18B, the magnetic yoke layer 2 has the yoke projecting portion 2A projecting toward the recording medium and a yoke setback portion 2B formed to set back from the yoke projecting portion 2A. Thus the spatial resolution of magnetic detection of the yoke-type magnetic head can be determined by adjusting the width and projecting amount of the projecting portion 2A.
In case of a CPP (current perpendicular to the plane) magnetoresistance effect element as shown in FIGS. 18A and 18B, the projecting portion 2A may be formed in agreement with an electrode formed on the magnetoresistance effect film 4.
In this type of yoke-type magnetic head, when a magnetic domain is generated in the magnetic yoke layers 2 and irregularly moves in response to a signal magnetic field, it produces noise. Therefore, a bias magnetic field is preferably applied to control the magnetic domain generated in the yokes 2. In case of the magnet head shown in FIGS. 18A and 18B, bias magnetic field applying films 6, 6 of a hard magnetic material are formed on opposite side surfaces of the magnetic yoke layers 2 to control the magnetic domain of the magnetic yoke layers 2.
The Inventors however, have found through their researches that a bias magnetic field from the bias magnetic field applying films 6 on opposite side surfaces of the yoke setback portions 2B may occasionally fail to reach the yoke projections 2A of the magnetic yoke layers 2 sufficiently. If the bias magnetic field is not applied sufficiently, then the magnetic domain irregularly moves in response to the signal magnetic field especially near the medium-facing surface, and noise is liable to occur.